1. Field of the Invention
The present invention relates to an organic light emitting display and a driving method thereof.
2. Description of the Related Art
Recently, various flat panel displays that have reduced weight and volume in comparison to cathode ray tubes (CRTs) have been developed. Flat panel displays include liquid crystal displays (LCDs), field emission displays (FEDs), plasma display panels (PDPs), and organic light emitting displays.
Among the flat panel displays, the organic light emitting displays make use of organic light emitting diodes that emit light by re-combination of electrons and holes. The organic light emitting display has advantages of high response speed and low power consumption.
FIG. 1 is a circuit diagram showing a pixel of a conventional organic light emitting display.
With reference to FIG. 1, a pixel 4 of an organic light emitting display includes an organic light emitting diode OLED and a pixel circuit 2. The pixel circuit 2 is coupled to a data line Dm and a scan line Sn, and controls the organic light emitting diode OLED.
An anode electrode of the organic light emitting diode OLED is coupled to the pixel circuit 2, and a cathode electrode of the organic light emitting diode OLED is coupled to a second power source ELVSS. The organic light emitting diode OLED generates light of a luminance corresponding to an electric current from the pixel circuit 2.
When a scan signal is supplied to the scan line Sn, the pixel circuit 2 controls an amount of electric current provided to the organic light emitting diode OLED corresponding to a data signal provided to the data line Dm. In order to do this, the pixel circuit 2 includes a second transistor M2′, a first transistor M1′, and a storage capacitor Cst′. The second transistor M2′ is coupled between a first power source ELVDD and the organic light emitting diode OLED. The first transistor M1′ is coupled between the data line Dm and the scan line Sn. The storage capacitor Cst′ is coupled between a gate electrode and a first electrode of the second transistor M2′.
A gate electrode of the first transistor M1′ is coupled to the scan line Sn, and a first electrode of the first transistor M1′ is coupled to the data line Dm. A second electrode of the first transistor M1′ is coupled with one terminal of the storage capacitor Cst′. Here, the first electrode is a source electrode or a drain electrode, and the second electrode is the other one of the source electrode or the drain electrode. For example, when the first electrode is the source electrode, the second electrode is the drain electrode. When a scan signal is supplied to the first transistor M1′ coupled with the scan line Sn and the data line Dm, the first transistor M1′ is turned on to provide a data signal from the data line Dm to the storage capacitor Cst′. At this time, the storage capacitor Cst′ is charged with a voltage corresponding to the data signal.
A gate electrode of the second transistor M2′ is coupled to one terminal of the storage capacitor Cst′, and a first electrode of the second transistor M2′ is coupled to another terminal of the storage capacitor Cst′ and a first power source ELVDD. Further, a second electrode of the second transistor M2′ is coupled with an anode electrode of the organic light emitting diode OLED. The second transistor M2′ controls an amount of electric current flowing from the first power source ELVDD to a second power source ELVSS through the organic light emitting diode OLED according to the voltage charged in the storage capacitor Cst′. At this time, the organic light emitting diode OLED emits light corresponding to the amount of electric current supplied from the second transistor M2′.
However, the conventional organic light emitting display may not always display images of desired luminance because of an efficiency change resulting from the degradation of the organic light emitting diodes OLEDs. In practice, as time elapses, the organic light emitting diodes OLEDs are degraded. As the organic light emitting diode OLED is degraded, light of gradually decreasing luminance is generated in response to the same data signal.